Coupling arrangement



Feb. 21, 1933. c. w. HANSELL COUPLING ARRANGEMENT Filed Sept; 21, 1927 4m j/rI 0 n 0 H a N 2 2 00 w. w 9 $0YN QSQRwQ RA 7/0 0/-' INPUT 70 OUTPUTRfS/STAA/C! INVENTOR CLARENCE W. HRNSELL BY I I J22 /m AT RNEY PatentedFeb. 21, 1933 UNITEDSTATES PATENT orricr.

CLARENCE w. rmnsnrr, or Ros n: 201m NEW YORK, ASSIGNOR ro arreCORPORATION or ensures, A corgronerron or DELAWARE COUPLING ARRANGEMENTApplication filed September 21, 1927, Serial No. 221,091.

This invention relates to coupling arrangements. d e pa u ar y t su h.M'- rangements used to change impedance and phase relation.

It is frequently desired to couple circuits together with a change inimpedance, as, for example, when matching theimpedance at the junctionsin branched transmission With very high frequencies it is not feasibleto obtain the desired impedance changes by the use of simple transformercircuits because insulation is so difiicult that reasonably closecoupling between the primary and secondary is impossible. To use aparallel resonant circuit and couple the output at variable tappingpoints on the inductance of the circuit makes it impossible to obtainzero phase shift, and is relatively inefficient for it involves highlosses owing to the circulating current in the resonant circuit.

Ithas been proposedto couple aseries circuit of inductive and capacitivereactances across one of the external circuits, and to couple the otherexternal circuit across either the inductive or capacitive reactance.This arrangement is satisfactory but has the disadvantage that there isinvolved an inherent phase shift the direction of which is determined bythat reactance across which the second external circuit is coupled, andthe magnitude of which is fixed for any given impedance ratio. It is anobject of my invention to provide a coupling arrangement which isefficient even at very high frequencies and which permits optionalimpedance change and phase shift.

To do this I change the impedance successively by means of cascadeconnected coupling circuits the impedance ratios of which are such thattheir product equals the desired ratio, and the phase shifts in whichare such that their algebraic sum equals the desired phase shift. In thespecial case of zero phase shift the arrangement comprises two of theseries circuits such as have been described, the impedance ratios ofwhich are equal to the square root of the desired overall impedanceratio, and the phase shifts in which are equal but opposite indirection, a 50 result which is obtained by coupling the second couplingcircuit to the first coupling circuit across either the inductive orcapaci tive reactance, and coupling the second external circuit to thesecond coupling circuit across the capacitive or inductive reactance,respectively. in The invention is described more in detail in thefollowing specification which is accompanied by a drawing in which itFigure 1 and Figure 2 represent known 60 coupling circuits; 8 i I Figure3 is a combination of known cir cuits embodying my invention;

Fi ure 4 is a graph which is useful when selecting the circuitconstants; and i i Figure 5 symbolically indicates an application of myinvention.

Referring to Figure 1 there is shown a series circuit comprising theinductances 2 and the capacitance 4, which are connected 7o by means ofthe terminals 6 to an external circuit. The terminals 8, connected tocondenser 4, lead to a second external circuit. The reactance values areso chosen that when the parallel circuit consisting of the resist: anceof the output circuit and the capacitance 4 is transposed to anequivalentseries circuit of capacitance and resistance the inductance 2resonates with the fictitious series capacitance, and the fictitiousseries resist+ 8o ance is equal to the desired line impedance. In thedirection from the terminals'fi to the terminals 8 the impedance isstepped up, but by connecting the circuit in the oppositeldirection theimpedance may be stepped down. 8;; Figure 2 is similar to Figure 1except that the terminals 18 have been connected to the inductivereactance 12 instead of to the capacitive reactance 14. In this casetheparallel circuit consisting of the resistance of Q0 the secondexternal circuit, that is, the circuit across the terminals 18, and theindlittance 12, may be transported into an equivalent series circuit ofinductance andresistance, and the capacitance 14 resonates with 95, thefictitious inductance, while the fictitious resistance is the desiredline impedance for the external circuit connected to the terminals 16. iIn Figure 4 the curve 20 shows the degrees 199 of phase shift betweenthe first and second external circuits as a function of the impedanceratio. It is clear that when employing circuits such as have been shownin Figures 1 and 2 the curve 20 is symmetrical, the phase shifts foreither the capacitive or inductive couplings being equal for a givenimpedance ratio, but opposite in direction.

Adverting now to Figure 3 it will be seen that in accordance with myinvention the coupling arrangement comprises a combination of thecircuits shown in Figures 1 and 2. In this manner if the impedanceratios are equal the resultant phase shift is zero. .Thus, in thespecial case where zero phase shift is desired the two circuits are sodesigned that the impedance ratio of each is equal to the square root ofthe desired ratio, so that the overall ratio is that desired, andmeanwhile the equal but opposite phase shifts in the two parts of thecoupling arrangement neutralize one another so that the resultant phaseshift is zero.

In the more general case the requirement for a desired impedance ratioaccompanied by a desired phase shift is met by combining circuits theproduct of the impedance ratios of which is that desired while thealgebraic sum of the phase shifts in which is that desired, whichinvolves factoring the desired product into those factors, from amongthe many possible groups of factors, which give the correct phase shift.This selection may be readily accomplished by the use of a chart such ashas been shown in Figure 4, the curves 22, 24, 26 and 28 of which areplotted to the same scale of ordinates and abscissae as the curve 20,but which represent overall impedance ratio as a function of overallphase shift when using the combined circuit shown in Figure 3. The curve22 is obtained by assuming that the impedance ratio of one of thecircuits is 0.2 and taking various values from zero to one for the othercircuit. The curve 24 is obtained by assuming that the impedance ratioof one of the circuits is 0.4 and taking various values for the othercircuit. Similarly c'urves 26 and 28 are obtained by assuming impedanceratios of 0.6 and 0.8 re spectively for one of the circuits.

The chart may be used as follows. A point representing the desiredimpedance ratio and phase shift is located on the chart, such as thepoint 30, located at an impedance ratio of 0.4 and a phase shift of 30degrees lagging. The point 30 is followed out on a line 32, approximatedfrom the nearest adjacent curve, until it intersects the curve 20, whichindicates the phase shift and the impedance ratio for one of thecoupling circuits to be 48 and 0.45. The impedance ratio of the other ofthe circuits may be obtained by dividing the desired ratio by the ratiofound for the first circuit, which comes out 0.89, or by subtracting thedesired phase shift from the phase shift in the first circuit to obtainthe phase shift in the second circuit, namely, 18 leading, and locatingthe impedance ratio for that phase shift on the curve 20, givingslightly less than 0.9, which is as it should be.

So, in Figure 4, the lines 34-and 36 represent the impedance ratio andphase shift for one of the circuits, while the lines 38 and 40 representthe impedance ratio and phase shift for the other of the circuits. Itwill be seen that the phase shifts differ by 30 degrees, and that theproduct of the impedance ratios equals 0.4, as was desired.

The chart as drawn serves only for values of ratio and shift which liewithin the boundaries of Y the curve 20, for it has been assumed thatthe circuits have phase shifts of opposite sense and impedance ratios oflike sense, which is the more usual case. It is clear, however, that thechart may be extended to include more general cases by continuing thecurves 22, 24, 26 and 28, which is done by taking impedance ratios forthe second circuit which are greater than unity. One such curve is shownin Figure 4, curve 22. To obtain ratios greater than unity one of thecoupling circuits in Figure 3 is re versed.

An application of my invention is indicated in Figure 5, in which thereare broadside antennae 102 and 104, with energized reflectors 106 and108, fed by transmission lines 110 and 112, which in turn are fed by atransmission line 114. Such antennae are described in a copendingapplication of Nils E. Lindenblad, Serial No. 229,407, filed October 28,1927. If the transmission lines 110 and 112 are similar to thetransmission line 114 their combined impedance is half of that of line114, and therefore impedances must be matched at the junction point 116.At this junction a phase shift is not injurious, and therefore the oldertype of coupling arrangements may be employed. But at the points 118 and120, where the line impedances also must be matched, the relative phaseof the energies supplied to the antennae 102 and 106 is of greatimportance, for their phase displacement should equal the natural phasedisplacement of the wave in space at points spaced at the distancebetween the antenna 102 and the reflector 106. To meet this requirementmy coupling arrangement may be applied at the points 118 and 120, andsimilarly at the points 122 and 124 for the other antenna.

I claim 1. The method of obtaining a desired impedance ratio and adesired phase shift which includes changing the impedance successivelyby ratios the product of which equals the desired ratio, andaccompanying the impedance changes with phase shifts the algebraic sumof which equals the desired phase shift.

2. The method of obtaining a desired impedance ratio with no phase shiftwhich includes changing the impedance by a ratio which is the squareroot of the desired ratio accompanied by a phase shift in one direction,and again changing the impedance by the square root of the desired ratioaccompanied by an equal phase shift in the opposite direction.

3. A coupling arrangement for obtaining a desired impedance ratio and adesired phase shift comprising a plurality of cascade connectedimpedance changing devices the procluct of the ratios of which equalsthe desired ratio and the algebraic sum of the phase shifts in whichequals the desired phase shift.

4. A coupling arrangement for obtaining a desired impedance ratio withno phase shift comprising a plurality of cascade connected impedancechanging devices having impedance ratios the product of which equals theratio desired, and the algebraic sum of the phase shifts in which equalszero.

5. A coupling arrangement for obtaining a desired impedance ratio withno phase shift comprising two impedance changing devices having equalimpedance ratios, and equal but opposite phase shifts, connected incascade.

6. An arrangement for changing impedance and phase by desired amountscomprising an external circuit, a coupling circuit connected thereto andhaving inductive and capacitive reactances in series, a second couplingcircuit having inductive and capacitive reactances in series coupledacross a reactance of one sign of the first coupling circuit, and asecond external circuit coupled across a reactance of another sign ofthe second coupling circuit.

7. An arrangement for changing impedance and phase by desired amountscomprising an external circuit, a coupling circuit connected thereto andhaving inductive and capacitive reactances in series, a second couplingcircuit having inductive and capacitive reactances in series coupledacross a reactance of one sign of the first coupling circuit, and asecond external circuit coupled across a reactance of another sign ofthe second coupling circuit, the coupling circuits having impedanceratios the product of which equals the desired ratio, and phase shiftsthe algebraic sum of which equals the desired phase shift.

8. An arrangement or changing impedance and phase by desired amountscomprising an external circuit, a coupling circuit connected thereto andhaving inductive and capacitive reactances in series, a second couplingcircuit having inductive and capacitive reactances in series coupledacross the inductive reactance of the first coupling circuit, and asecond external circuit coupled across a capacitive reactance of thesecond coupling circuit.

9. An arrangement for changing impedance and phase by desired amountscomprising an external circuit, a coupling circuit connected thereto andhaving inductive and capacitive reactances in series, a second couplingcircuit having inductive and capacitive reactances in series coupledacross the inductive reactance of the first coupling circuit, and asecond external circuit coupled across the capacitive reactance of thesecond coupling circuit, the coupling circuits having impedance ratiosthe product of which equals the desired ratio, and phase shifts thealgebraic sum of which equals the desired phase shift.

CLARENCE W. HANSELL.

